Process for the manufacture of chromium compounds



gust 24, 1925, N0. F. 59,650 IV 12 m;

Patented Aug. 6, 1929.

UNITED STATES PATENT OFFICE.

PAUL WEISE, 0F WIESDORF, NEAR COLOGNE-ON-TIfE-RHINE, GERMANY, ASSIGNOR TO I. G. FABBENINDUSTRIE AKTIENGESELLSCHAFT, OF FRANKFORT-ON-THE-MAIN,

GERMANY.

PRO CESS FOR/THE MANUFACTURE OF CHROMIUM COMPOUNDS.

Ho Drawing Original application filed March 6, 1926, ,Serial No. 92,937, and in Germany August 24, 1925.

' Divided and this application filed October 25, 1926. Serial No. 144,192. 7

I have filed applications in German Aurance, .April 15, 1926, application No. 218,535; England, February 8, 1926, application No. 3,553;

Czechoslovakia, February 8, 1926, applica tion P. 681 Belgium, April 17, 1926, application No. 264,386; and in Russland, February 24., 1926, application No. 7,159.

The processes for the manufacture of chromium compounds from chrome ore em ployed in industr up to the present time suffer from the disadvantage that they involve losses of ore which are very difficult to recover. According to most of such. processes a diluent is added to the mixture of chrome ore and alkali, as for example chalk, dolomite, iron oxide, etc.,' these substancesbeing only recoverable in exce tional cases In most cases they are comp etely lost with the unattacked ore, thus causing a considerable increase in the cost of the process. Proposals have already been made for using as diluents such materials as can be recovered in a form available for further use. Thus the German Patent No. 166,767 suggests the use of finel crushed chrome ore but the process, accord ing to this patent is restricted to the joint use of a hand fed furnace. In orderto obtain a satisfactory attack, when working with me chanical furnaces, and with 'mixtures of finely crushed chrome ore and alkali metal carbonates or hydroxides, very large amounts of ore in proportion to the material used for attacking the ore must be employed, as for example six times the quantity of finely crushed o re. This is due to the fact that a certain amount of diluent material must be 7 present in order .to render the melt sulficiently porous, so that the air-oxygen refactory working can be achieved with a much smaller quantity of ore acting as the diluent material and to prevent caking if ore of a definite grain size is employed. In this manner only the most finely crushed portions of I the ore arefpreponderantly attacked while the coarser portions remain practically untogether/ofi the charge. The application of my invention increases the productive capacity of the whole process concerned.

' 1 The method of working is as follows The moist or dry mixture 'of'an ore which leaves a residue of 1530% on a sieve of 70 mesh per cm. with so much of the decomposition agent that the content of the same amounts to 2832%, is heated in an oxidizing atmosphere to the reaction temperature of over 1100 C. The sintered melt is leached with water, advantageously in the presence of a small amount of acid in order to decompose the aluminate. The achromate which then passes into solution is separated from the residue and worked up in the customary manner.

The residue after they leaching operation consists of unattacked chrome ore, alumina, magnesium and iron-oxide. For the recovcry of the unattacked chrome ore mechanical methods may be employed, as for example the concentration of the acid should not be too high, as otherwise the final liquors obtained are diflicult to filter. Particularly favourable are acids of about 30 B. Sul

furic acidof from 5 B.-to 30 B. may be used. It is likewise advantageous to modera ately' heat the acid although it is advisable not to allow the temperature to rise above 60 G. In general temperatures ranging from atmospheric temperature, 15 C. up to 60 C. may be employed. If these conditlons are taken into account a residue is obtained which can be filtered ofi quite easily.

The amount of acid employed may vary within wide limits, either the theoretical amount, an insufiicientamount, or an excess, may be employed. 7

When using the theoretical quantity of acid the final liquors obtained are difiicult to filter and this method is therefore only se- I altered and serve'as diluent material thus lected in special cases.

i preventing the-otherwise unavoidable caking When an insuflicient quantity of acid is employed the recovered chrome ore still contains corresponding quantities of iron and magnesium oxides. A proportionate quantity of acid may be added in order to maintain the content of these impurities the same or by varying the acid the amounts of the impurities may be allowed to increase. In the latter case the possibility arises that the melt may become so enriched in iron and magnesium oxides that the decomposition agents added to the charge may just succeed in attacking the wliole of the available chrome ore. The resulting residue is then practically free from chromium and may be thrown away.

By the application of an excess of acid pure ore is invariably recovered.

When using either an insufiicient quantity of acid or an excess of acid the liquors obtained can be filtered with ease. The velocity of reaction is very great in all cases.

The recovered ore, with or without the addition of fresh ore, is brought to the desired grain size by means of suitable appliances and returned to the charge.

The following examples will serve to illustrate my invention Example 1.70 parts of ground chrome ore of any composition leaving a residue of 25% on a sieve of 70 mesh per cm., are intimately mixed with parts of sodium carbonate. According to' the construction of the revolvino' furnace and the feeding arrangement, the mixture may be introduced into the furnace either moist or dry and there heated in the customary manner to 'above -1100 C; The resulting melt is quenched in water, allowed to soak and the chromium liquor leached and separated from the water-insoluble portion. For the purpose of recovering the unattacked chrome ore, this water-insoluble portion is treated with so much sulfuric acid of 15 B. at C. that not all the iron and magnesium oxides are dissolved; the weakly arated off and the residue dried. This resibasic liquor is sep-.

due is mixed with a fresh su ply of ore of the required grain size and wit sodium carbonate and returned to the furnace. The amount of sulfuric acid required as the process proceeds should be always adjusted so that the basicity of the liquor remains always the same. The yield of chromate obtained is about 90% calculated on the amount of sodium carbonate used.

Emample 2.-The water-insoluble portion as obtained in Example 1 after the separation of the chromate liquid is treated with sufficient sulfuric acid of about 20 B. in the cold that after the dissolution of all the undesirable impurities a slightly acid solution remains. The heat of reaction leads to a temperature of about 50 C. without special heating. The recovered ore can be employed in a fresh charge without further treatment. v

Example 3.The water-insoluble portion obtained according to Example 1 is treated with sulfuric acid according to the countercurrent principle. Thereby the almost extracted ore comes into contact with fresh acid, and thus the acid may be selected of any desired strengthf As the process of extraction proceeds further. the most suitable dilution can be easily adjusted by the addition of water.

This application is a division of my application Serial Number 92,937, filed March 6, 1926.

I claim In the manufacture of chromium compounds by heating an excess of chrome ore with an alkaline agent and leaching the chromium compounds out of the reaction mass, the step which comprises preparing the residue after leaching for reuse in the process by treatment with an excess of acid.

In testimony whereof I have hereunto set my hand.

/ PAUL WEISE. 

